1. Field
The present patent application for industrial invention relates to a mold for footwear bottoms and other manufactures composed of two overlapping layers of expandible and reticulable polyolefin materials.
The invention has been devised with the specific intention to innovate and rationalize the production modes of a type of footwear bottoms that already exists on the market.
2. Description of Related Art
Reference is made to footwear bottoms formed of two overlapping layers made of expandible and reticulable polyolefin materials provided with different characteristics.
It may sometimes happen that the upper layer, which is designed to come in contact with the user's foot, needs to be softer and more comfortable and the lower layer, which is designed to interfere with the ground during walking, needs to be harder and more resistant to wear.
Special molds have been traditionally used for the realization of similar “double layer” bottoms, which are composed of two lids, each of them with corresponding cavity, designed to be interfaced with interposition of an intermediate closing plate.
Such a plate is able to simultaneously close the downward cavity of the upper lid and the upward cavity of the lower lid.
After suitably arranging such a mold, the two expandible reticulable polyolefin materials are hot injected, at fluid state, inside the cavities of the corresponding lids.
As it is known, in view of the high temperature, these materials are subject to a process defined as “reticulation”, which causes a considerable increase in volume.
This allows said materials to exactly fill the cavities of the lids and be perfectly molded inside them.
Before completing the reticulation process, the two lids are separated and the closing intermediate plate is removed.
Immediately afterwards, the two lids are placed one against the other, in such a condition to perfectly interface their cavities.
A further consequence of said operation is that the lower side of the layer of expandible reticulable polyolefin material that is still contained in the cavity of the upper lid is brought directly in contact against the upper side of the expandible reticulable polyolefin material that is still contained in the cavity of the lower lid.
Considering that the two layers of expandible reticulable polyolefin materials are still in reticulation phase and tend to increase additionally in volume, it appears evident that mutual penetration is formed between said contact surfaces, corresponding to irreversible connection.
Whereas it is true that such a technology has proved rather reliable from the technical-functional view point, it has been quite unsatisfactory in terms of aesthetics.
In particular, such an aesthetical drawback appears when the aforementioned technique is used to produce a footwear bottom composed of two overlapping layers of expandible reticulable polyolefin materials with different color.
In such a case, in fact, said penetration between the contact surfaces of the two molding materials causes the inevitable mutual contamination of the two colors.
In view of the above, the line that should mark the separation between the two overlapping layers on the perimeter side of the bottom acquires an indefinite irregular color, which is extremely inadequate for the aesthetical pleasantness of the bottom.